The invention relates in general to seals and more particularly a seal for separating grease and oil in the region of a bearing and to an assembly containing such a seal.
The drive axle of a typical large over-the-road or off-road truck has axle shafts which extend through tubular axle housings from a differential and at their ends are connected to wheel hubs which rotate about the ends of the axle housings on antifriction bearings. Usually, these bearings are tapered roller bearings which require lubrication for their successful operation. The other road wheels of such vehicles likewise usually rotate on tapered roller bearings, which are often package-sealed for life, but these bearings are simply mounted on spindles. The traditional lubrication for the spindle-mounted bearings for these other road wheels is grease. After all, grease remains along the critical surfaces where it is required, even when the bearing is at rest, and further is easily retained by seals. Moreover, the grease seals remain effective for extended periods of time, much longer than oil seals.
But many drive axles, particularly those designed for large trucks, rely on the differential lubricant, which is a gear oil, to sustain the wheel bearings. The differential housing serves as a reservoir for this oil which migrates through the tubular axle housings to the wheel bearings. This is not a totally reliable source of lubrication, and when interrupted, the results can be disruptive and costly. Apart from that, oil being harder to retain than grease, more readily passes the seals which are designed to retain it within the bearings, and oil emerging from wheel bearings often finds its way onto the brake shoes where it adversely affects the operation of the brakes.
One does not derive all of the benefits of grease lubrication simply by packing traditional oil-lubricated bearings on drive axles with grease. The oil is still present and it mixes with the grease, thereby thinning the grease and in effect returning the bearings to their former oil-lubricated condition.
The present invention resides in an assembly including a bearing that exists in the presence of oil, yet is lubricated by grease, with a seal isolating the grease from the oil. Indeed, the seal pumps one or the other of the lubricants toward its source, and preferably both toward their respective sources, that is the oil away from the interior of the bearing and the grease toward the interior of the bearing. The invention also resides in a seal having the capacity to pump in two directions.